The use of photo sensitive sensors, such as image sensors, in modern digital cameras and video recorders is well known. Generally, an image sensor is comprised of an array of individual sensors arranged in a series of columns, each column having a plurality of individual sensors that themselves are row elements. Each of the individual sensors has a storage element to maintain a value representing the image detected by that sensor. Typically the storage element will be one of either a capacitive element which stores a charge representing the image value, or memory to store a digital representation of a charge representing the image value.
The term column is used herein as a general term referring to the minimum repeated structure in one dimension of a sensor array, with the other dimension being the row. For example, it is common for image arrays to have a repeated column structure resulting in the image arrays being manufactured in a modular fashion. Image arrays manufactured in a modular manner are designed by duplicating a smaller design. For example, a manufacturer may design a specific image array module to have sixty-four (64) columns. If a larger array is desired, such as an array with five hundred and twelve columns (512) the 64 column design module would be repeated eight times. It is well known that when a modular technique is used, it is common for specific elements within the base design, e.g., the 64-column design module, to have errors which are repeated within each design module duplication. This results in a repeating error in a modular fashion across a larger array. For example, it would be possible for an error to occur in the second column of each base design module resulting in a repeating error every 64 columns, e.g. at column two of the reference design module. This repetition of errors is referred to as repeating Fixed Pattern Noise (FPN) within the photosensitive array. In other words, because these errors are “Fixed” with respect to a particular column or pixel within a column, they are predictable and can therefore be predictably corrected, while the “Noise” is with respect to the system, and reduces the quality of the image as a whole. It will be appreciated while the minimum repeated structure herein is assumed to be a column, that sensors can be made that would have the minimum repeated structure being a row. For purposes herein, the term column is used throughout to refer to the minimum repeated structure in one dimension of a sensor array whether a row or a column.
Manufacturers have compensated for the repeating fixed pattern noise errors in a number of manners. One solution used by manufacturers has been to provide a fixed pattern noise error register for each column in an array whereby the register associated with the specific column would have a stored error correction value to correct the noise associated with that column. It should be noted that typically the noise associated with the column would be applied to each storage element in the entire column. While effective, the design costs of implementing a storage location for each column in a photosensitive array is large, thereby resulting in increased design cost.
An alternative to correct repeating fixed pattern noise has been to provide a smaller number of registers associated with the modular size of the photosensitive array which is used in a repeating fashion. For example, where the base reference design for the photosensitive array is 64 columns, only 64 register values would need to be used. While this provides improved efficiency, it still requires more memory storage capability than is generally required by a specific design.
In addition to the repeating fixed pattern noise errors, non-repeating, or random, fixed pattern noise errors also can occur in specific columns. A non-repeating fixed pattern noise error refers to those errors that do not repeat in a modular fashion across the array, but are fixed with respect to their location within the array of a specific sensor. Typically, such errors are the result of unique manufacturing defects or flaws at a specific point of a device being manufactured. Typically such non-repeating fixed pattern noise errors have been corrected by of specific software applications, thereby increasing the complexity of final application software support.
It should now be apparent that an improved method and system of fixed pattern noise reduction would be useful.